(a) Field of the Invention
The present invention relates to a keypad for a portable telephone and a manufacturing method thereof. More specifically, the present invention relates to a keypad in which film and silicone rubber are integrated in a singlebody structure to manufacture the keypad.
(b) Description of the Related Art
Certain types of electronic equipment such as calculators, telephones or a portable telephone require a means of inputting data. A common structure providing this capability is comprised of a front housing and a keypad, the keypad being assembled into the housing such that buttons, or keys, of the keypad protrude through holes provided in the front housing.
A conventional keypad used in a portable telephone has dome switches which contact a printed circuit board in response to key operation. The conventional keypad may be made of plastics (film type keypad) or silicone rubber (silicone rubber type keypad).
The silicone rubber type keypad is formed by an injection molding process in which silicone rubber is used. After injection molding, characters such as numerals, letters and symbols are printed on an outer surface of the keypad. A drawback of the silicone rubber type keypad is the likelihood that the characters will discolor or rub off after a period of use.
The film type keypad is formed by an injection molding process in which plastics are used. After injection molding, a film on which characters are printed is attached to the keypad. Since characters are printed on an interior surface of the film, they do not discolor or rub off with use. However, because the film type keypad is made of hard plastics, it is not as agreeable to the touch as a keypad made of a pliant material such as silicone rubber.
The inventor of this application disclosed a keypad and method for overcoming the aforementioned problems in Korean Patent Application No. 98-63310 filed on Dec. 31, 1999. In the method of this patent application, after a film, which is pre-formed into a key shape, is coated with epoxy, the film filled with silicone rubber. However, after the epoxy is cured, the epoxy becomes overly hard such that the keys are difficult to operate. It also takes long time to fabricate the keypad.
In view of the prior art described above, it is an object of the present invention to provide a keypad and a manufacturing method thereof in which a time for fabricating the keypad is minimized by extruding a film and silicone rubber in a single mold.
It is another object of the present invention to provide a keypad and a manufacturing method thereof in which slits are provided around keys to provide enhanced operation feel to the user and prevent keys adjacent to the user-targeted key from being depressed.
To achieve these objects, as embodied and broadly described herein, the invention comprises the steps of
printing characters on a transparent, planar film;
preforming the planar film through a pressing process such that the planar film has a predetermined shape including a plurality of depressions;
punching slits in the pressed planar film around the depressions;
filling liquid silicone rubber into the depressions of the pressed planar film;
forming a keypad by pressing the silicon rubber in a metal mold so as to fabricate an integrated keypad in which keys are interconnected; and
trimming an outer periphery of the formed keypad according to a predetermined keypad shape.
In the pre-forming process, grooves are formed in the planar film in which light emitting devices are located. It is preferable to use a hot press in the pre-forming process, which is heated to a predetermined temperature such that a uniform film thickness is maintained and a distortion of the characters caused by film expansion is prevented.
Also, to achieve these objects, the present invention provides a keypad for a portable telephone, comprising a printed circuit board having a plurality of contacts; a plurality of dome switches disposed on the printed circuit board; a plurality of keys for pushing the plurality of dome switches; and a plurality of light emitting devices, displaced between the plurality of keys, for backlighting.
In the keypad, grooves are formed between the plurality of keys to enable the placing of the plurality of light emitting devices thereon.
Both foregoing general description and the following Detailed Description are exemplary and are intended to provide further explanation of the invention as claimed.